Lift is basic to flying. In order for an airplane to fly, Lift must be greater than Gravity. As an airplane moves forward, the wing produces Lift.

When you examine an airplane's wing, also called an airfoil, you'll notice that the top front part is curved and the bottom part is relatively flat. This special shape creates Lift, which makes the airplane fly.

As the wing moves forward, the air flowing over the top travels faster than the air flowing beneath, resulting in a lower pressure area above the wing. The relative pressure differential provides the upward force called Lift.

For an airplane to maintain level flight at a particular altitude, Lift and Gravity must be equal. When Lift is greater then Gravity, the airplane will ascend. When Gravity is greater than Lift, the airplane will descend.

The force of forward movement is called Thrust created by the engine-driven propeller or a jet engine.

The force of Drag works opposite the force of Thrust.